Para-glycidyloxystyrene (pGS) is a monomer with great versatility and utility due to its epoxy functionality and its superior thermal, chemical, and hydrolytic resistance relative to the most commonly used epoxy-containing vinylic monomer, glycidyl methacrylate. The epoxy functionality is highly useful for curing and adhesion. For example, pGS monomer may be used as a functional component of coatings, adhesives, films, plastics, resins, elastomers, automotive finishes and inks, as well as in electronic materials. Also homopolymers or copolymers of pGS will provide materials with advantages in performance and versatility.
A number of methods for the chemical synthesis of pGS are known. However, these methods require starting materials that are difficult to prepare and are not commercially available, are expensive, and/or require multiple steps. For example, U.S. Pat. No. 6,255,385 discloses a two-step process for the synthesis of pGS starting from 4-hydroxybenzaldehyde, with an overall 20% yield for the two steps. IT705414 discloses the synthesis of pGS also starting with 4-hydroxybenzaldehyde, in which multiple steps were required to synthesize the para-hydroxystyrene intermediate, which is purified prior to further reaction. The conversion of para-hydroxystyrene to pGS is performed with a strong excess of epichlorohydrin in the virtual absence of water, with continuous distillation to remove water as it forms in the reaction. A one-step process for the synthesis of pGS starting from acetoxystyrene is described in Hashimoto ((1987) J of Polymer Science, Part A:Polymer Chemistry 25:2827-2838). The cost of acetoxystyrene makes this method commercially unattractive.
Though pGS has been made from p-hydroxystyrene (pHS), pHS is available commercially only in small quantities, and is available in a form unsuitable for glycidyloxylation (in 10% ethylene glycol) or as pure pHS, which is fairly unstable and very costly. U.S. Pat. No. 5,274,060 describes a method for preparing 4-hydroxystyrene starting with pHCA. In that method, the pHCA is decarboxylated in dimethyl sulfoxide in the presence of an amine catalyst, i.e., 1,8-diazabicyclo[5,4-0]undec-7-ene, and hydroquinone at 135° C. to give 4-hydroxystyrene. The yield in that method was 63%.
Monomers of pGS have been polymerized with AIBN as initiator at 80° C. (Tanimoto et al. (1968) J. Syn. Org. Chem. Jpn. 26:1102-1106), or by cationic initiators with selective polymerization of the vinyl group and not the epoxide using HI/I2 (Hashimoto et al., (1987) J. Poly. Sci. Part A Polym. Chem. 25: 2827-2838). Also pGS was copolymerized with vinylpyridines at 60° C. in THF initiated by AIBN (Tanaka (1979) ACS Symposium Series 114 (epoxy resin chemistry):197-210).
The thermal decarboxylation of substituted cinnamic acids has been studied in aqueous media. Pyysalo et al. (Lebensmittel-Wissenschraft u. Technol. 10 (Food Science and Technology):145-147 (1977)) describe the thermal decarboxylation of substituted cinnamic acid derivatives at pH 1 to 6 at 100° C. in aqueous buffer. Cohen et al. (J. Amer. Chem. Soc. 82:1907-1911 (1960)) describe the thermal decarboxylation of p-hydroxycinnamic acid in aqueous buffers at pH 1 to 12.
Thermal, base-catalyzed decarboxylation of phenolic substrates followed by acetylation in a single reaction vessel, two-step process is disclosed in US 20050228191.
The need exists for a method for preparing GS monomers and polymers thereof that uses relatively inexpensive reagents, is relatively simple, and results in high yields. Applicants have solved the stated problem by discovering a simple method for preparing pGS starting with para-hydroxycinnamic acid (pHCA) which involves an HSM intermediate that does not require isolation.